The AM Forum

Item:   A Hammond catalog from 1935 lists the 10-300 choke as having 4000 volt insulation.

Item:   A Hammond catalog from the  '50s lists the 10-300 choke as rated for 800 volts operating, with no comment on insulation strength.

I assume that if the choke had changed its insulation characteristics, the company would NOT have kept the same part number, ergo they are one and the same choke.

Is that assumption valid?

Comments?

al@w8vr.org
www.w8vr.org

I wouldn't make that assumption.

The other transformer vendors of that era (e.g., Thordarson, Stancor, UTC) somtimes changed product specs and kept the same numbers.

I don't know specifically about Hammond.

Dave

Thank you Dave.

If you can give a specific example of a transformer or choke that maintained its part number although the specs had changed, I'd like to study the issues.

-al hart, w8vr

maybe a silly question, but do the insulators look like 800V or 4000V ones? Not that all 4000V chokes have ceramic cones.. some just have a big piece of material and two terminals well away from the edges.

Ask them as they are still in business and might have the drawings.

Carl

OK, look at the UTC S-35 chokes. In the 1949 catalog they were listed as 20hy, but by 1955 they were 8hy.

The Stancor C-1415 were 6hy @ 7500V in 1948 but were 8hy @ 5000v in 1939.

I also have a Thordarson power transformer (I forget the number) that is listed at two different output voltages depending on which year's catalog you look in.

I have Merit A-3110 modulation transformer that has different impedance ratios listed in the 1951 catalog than the ratios listed on the label on my transformer. I also have a Merit filament transformer that has different voltage specs from one catalog to another.

800 volt operating and 4000 volt insulation are two different type ratings.  Usually chokes are rated with a RMS test voltage.  A choke with a 5KV RMS test voltage rating is good for about 2KV RMS operating.  The rule for RMS test rating is to subtract 1KV and then divide by two.  I never could figure how to tell what a voltage insulation rating means as to how high a voltage can be used.

Voltage operating ratings mean just that.  800 volts operating is for a 800 volt supply, maybe it go a little higher without problems.  Some voltage operating ratings may be a DC rating.  The choke will be labeled DC operating.

Input chokes have higher peak voltages on them than a second choke would have in a LCLC filter.

The Stancor C-1415 chokes were made differently.  The early ones were not potted and rated 5KV RMS test.  The later ones were potted and rated 7.5KV RMS test. I have some of each type.

Fred